It is well known that in motor vehicles with internal combustion engines which are coupled to an automatic transmission, the jolt during shifting of the transmission can be decreased substantially by decreasing the engine torque.
For example, in British Pat. No. 929 621 apparatus is described in which the shift signals for up-shift operate a monostable multivibrator which causes a temporary closing of the throttle valve.
In the system shown the DE-PS No. 10 80 415, the control apparatus for the automatic transmission consists of a mechanically operable switch which is closed when a control shaft is in a particular position. When the switch is closed, it operates a relay and a solenoid which in turn control the linkages to the throttle valve of the engine or to the ignition system.
In the apparatus of DE-OS No. 14 80 177, the shift command electromagnetically activates a pawl which blocks the fuel supply during the shift until the synchronous operation of the gearing has been reestablished.
Reduction of engine speed during gear shift by a retiming of the ignition is illustrated in DE-AS No. 16 26 427. A delay circuit is provided which, upon initiation of the shift, delays the spark generation.
In the apparatus described in French Pat. No. 1 524 354, a timing unit is provided which interrupts the fuel supply for a predetermined time interval during gear shift.
Similarly, the system illustrated in DE-AS No. 21 09 620 causes an interruption of the fuel injection together with activation of the solenoid causing the gear change, but delayed relative thereto.
DE-AS No. 21 63 979 teaches the system wherein the up-shift command signal of the automatic transmission is differentiated, the differentiated up-shift signal being applied to a computer which in turn decreases the width of the injection pulses during the gear shift.
All of the above-described systems for reducing a motor torque during gear shift have the common disadvantage that the time at which the reduction of torque is to take place depends upon the time that the shift command is initiated and, therefore, means have to be provided which signal the initiation of this shift command.